The present invention pertains generally to magnetic tape drives, and more particularly to a method and apparatus for precisely positioning a cleaning wheel against a recording drum in a magnetic tape recording system.
In a magnetic recording system that uses a motor actuated mechanical gear, rack, and pinion system to position a felt cleaning wheel against the recording drum, the prior art presents two types of solutions. In the first solution, a precision positioning mechanism is used to maintain a constant contact force against the drum. This solution is problematic in that it is costly in terms of components and engineering design time, which therefore increases the overall cost of the system.
In today""s competitive recording technology market, where the difference in a few dollars between competitive product can give a company an edge over its competitors, solutions for lowering the manufacturing costs of the product are continually sought out. Accordingly, many lower-cost tape drives employ a low cost cleaning wheel positioning mechanism instead of the more precise and costly mechanism described above. This system is essentially an open-loop system which actuates a cleaning wheel positioning motor in proportion to a predetermined fixed positional target in the cleaning wheel transport mechanism. The cleaning wheel is positioned to the fixed positional target along the path of the cleaning wheel transport mechanism. The relative position of the recording drum is not sensed, and the mechanical tolerances of the system play a large role in how precise the positioning can be done. The fixed positional target is individually calibrated at the factory for each drive since, due to component tolerance variance, the distance between the drum and cleaning wheel in individual drives can vary. However, this open-loop approach is problematic since between repeated cleaning operations on any given drive, the distance between the drum and cleaning wheel can vary due to excessive gear backlash and other mechanical imprecisions. This cleaning operation positioning variance often results in the cleaning wheel not contacting the drum at all during a cleaning wheel xe2x80x9ctouchxe2x80x9d operation, or in the cleaning wheel pressing too hard against the drum thereby resulting in damage to the recording heads, the drum surface, and to the cleaning wheel itself.
Accordingly, a need exists for a more precise and less costly technique for positioning the cleaning wheel against the recording drum during a cleaning operation. It would be desirable that this technique operated consistently from tape drive unit to tape drive unit and over temperature and voltage variations. Furthermore, it would be desirable to have such a technique without requiring additional components.
The present invention is a novel method and apparatus for precisely positioning a cleaning wheel against a recording drum during a cleaning operation. In particular, the present invention allows cleaning wheel positioning control that is consistent from drive to drive and over varying temperature and manufacturing process variations. Furthermore, the present invention allows precise control without requiring additional components that add to cost, complexity, and test time.
In accordance with the invention, in a tape drive mechanism that actuates the cleaning wheel against the recording drum during a cleaning operation, the contact pressure between the cleaning wheel and recording drum during a cleaning operation is controlled by constantly monitoring the recording drum drive motor current (and/or closed loop speed control voltage). While sensing the drum voltage/current feedback, the cleaning wheel is slowly transported towards the recording drum until an increase in drum motor drive voltage/current is detected. The increase in drum motor drive voltage/current is cause by the increased torque load incident on the drum as a result of the contact pressure between the drum and cleaning wheel. This method eliminates the need for precisely determining a fixed positional target for the cleaning wheel transport and its associated individual drive calibration at the factory. It also effectively and inexpensively provides precision-controlled contact force between the cleaning wheel and drum while remaining completely immune to positioning inaccuracies due to component tolerance variances from drive to drive and between cleaning operations.